1. Field of the Invention
The present invention relates to a plasma processing method and a plasma processing apparatus.
2. Description of the Related Art
With improvement in the degree of integration of semiconductor devices, heavy metal contamination in a process chamber is becoming an increasingly important problem in the processing of a silicon semiconductor wafer (hereinafter, referred to as a “wafer”) and in the process of manufacturing a device. The heavy metal may be diffused and dissolved in a film on the wafer by a heat treatment to form a pair with a dopant that is generated when manufacturing a transistor or form a precipitate of the heavy metal, a stacking defect or the like. As a result, deterioration of withstand voltage of an oxide film or increasing of a leak current may occur.
Occurrence of the heavy metal contamination by chromium (Cr) depends on a performance or capability of a plasma processing apparatus. If a member containing Cr (hereinafter, referred to as a “Cr containing member” as well) is included in a plasma processing apparatus, a reaction product of Cr may be deposited on an inner wall of the process chamber when performing an etching process. The heavy metal contamination by Cr generated at this time causes a large influence on a performance of a semiconductor product and also lowers yield.
In order to reduce the heavy metal contamination by Cr, it can be considered to change a hardware structure of a plasma processing apparatus. However, there is a drawback in cost in order to improve the hardware structure of the apparatus, because the development cost increases. Thus, it is desired to reduce the contamination by Cr without changing the hardware structure of the apparatus.
For example, Patent Document 1 provides a technique in which, after performing plasma cleaning of an oxygen (O2) gas under an etching condition where less deposition occurs and before starting etching, a film is deposited on an inner wall of a process chamber by plasma of a perfluorocyclobutane (C4F8) gas and an argon (Ar) gas. With this configuration, the inner wall of the process chamber is protected from the sputtering in the etching by the deposited film and beating out of the contamination from the inner wall to be adhered to the wafer can be prevented.
However, Patent Document 1 does not disclose what kind of substances the contamination includes, and does not disclose a method of preventing the heavy metal contamination in the process chamber when the reaction product generated by the plasma etching contains Cr.